June 4, 2019
Without preamble, let's talk about non-destructive pressure vessel testing. Long story short, vessel welds are not exposed to damaging sampling energies when they're inspected by NDT (Non-Destructive Testing) equipment. Now, done with the generalities from the outset, you'll be taking a look at Radiographic Testing (RT). A little like the X-Ray machines used in hospitals, this technology uses penetrating electromagnetic rays to examine a realm that's normally concealed.
Radiographic Testing: Pressure Vessel NDT
Broadly speaking, the equipment uses invisible, metal-penetrating electromagnetic radiation to "see" inside the welds and walls of pressure vessels. The electromagnetic rays are absorbed, reflected or influenced in some manner. When the altered rays return to a radiation-sensitive phosphor plate, any and all potential defects are exposed. Again, let's cut back on the oversimplifications, at least for today. In more detail, there are several different types of radiographic testing available. Short wavelength X-Rays are used to examine pressure vessels for concealed discontinuities. Gamma rays are also used in this field of NDT inspecting.
Spot and Full Radiography Comparisons
Traditional RT work uses the phosphor plate method. Computed Radiography loads a phosphor-treated cassette into a special test assembly, which then analyses the differently exposed sections. Scanned by laser, an image is produced of X-Ray or Gamma Ray exposed weld cores. There's also a real-time form. This equipment digitizes the radiation profiles and transforms the signal into an optically viewable image. Rendered on a computer monitor, subpar welds are viewable in real-time. However, there's a problem. Carrying out a full Radiography Testing procedure, hundreds of shots would be required if an entire pressure vessel were to be inspected. Alternatively, spot radiography work targets critical welding junctures and key stress seams.
The Future of Radiography Testing
Does this technology have a future? Due to the high radiation levels, other NDT technologies are taking over. Ultrasonic testing has already been suggested as a viable replacement for R.T. inspection. If low energy solutions make themselves known, Radiography will obviously continue for some time, as it's a well-established inspection method. And, used under controlled conditions, the health and safety concerns can, of course, be safely mitigated. All the same, ultrasonic NDT technology is the safer, more portable and health-friendly solution.
As a barebones description, Radiographic Testing emits bursts of short-wave electromagnetic radiation. The tiny peaks and troughs of the waves easily penetrate pressure vessel surfaces. Even so, the spot and full inspection non-destructive testing procedure are mostly used to assess weld integrity. There are other, more precise, instrumentation types, including those that use fluxing magnetic currents used to test pressure vessel sheets for microcrystalline discontinuities.
Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619
1865 Frankston Flinders Road,
Hastings, VIC 3915
Ph: (03) 5909 8218
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